Cathode ray tubes (CRT's) are used as displays for television sets and computers. To generate a display picture, an electron beam scans across a phosphor screen, causing the phosphors in the screen to emit various colors of visible light. In many cases, a deflection yoke is used to deflect the electron beam through a scanning pattern.
As shown in FIG. 1a, a conventional deflection yoke 10 has a funnel shape for mating with a CRT 12. The CRT 12 has a neck portion 14 that fits inside a corresponding neck portion 16 of the deflection yoke. Both the neck 16 of the deflection yoke 10 and the neck 14 of the CRT 12 have a generally frusto-conical shape, but the conical shape of the deflection yoke's neck 16 is somewhat shallower and wider to allow adjustment of the yoke's 10 position with respect to the CRT 12. Thus, when the deflection yoke 10 is placed on the outside of the CRT 12, it can be adjusted in both the vertical and horizontal directions while still remaining around the CRT 12. Once the optimum deflection yoke 10 position with respect to the CRT 12 is achieved, the deflection yoke's 10 position must be fixed to ensure that its orientation with respect to the CRT 12 is permanent.
The most common method for fixing the deflection yoke's 10 position is by inserting hard rubber wedges 18 in between the CRT 12 and the deflection yoke 10, shown in FIG. 1b. Because the wedges 18 often must be inserted manually, the process is quite inefficient and slow by today's manufacturing standards. In addition, it is quite difficult to maintain ideal deflection yoke 10 alignment on the CRT 12 using this method because the insertion of one wedge 18 could cause the deflection yoke 10 to shift slightly with respect to the CRT 12, possibly placing the deflection yoke 10 at a less than an optimal position once all of the wedges 18 are inserted.
Another proposed solution is to form openings in a separator of the deflection yoke and push plastic slides through the openings (not shown), but this presents many of the same problems as the method using rubber wedges 18. Further, it has the added disadvantages and costs associated with creating plastic slides that fit precisely into the openings in the deflection yoke separator to ensure that the deflection yoke 10 does not shift on the CRT 12 after assembly.
To create a more precise fit between the CRT 12 and the deflection yoke 10, some manufacturers inject an adhesive or a liquid polymer 19, such as glue or epoxy, in between the CRT 12 and the deflection yoke 10, as shown in FIG. 1c. The adhesive fills and conforms to the shape of the space in between the CRT 12 and deflection yoke 10, ensuring a tight seal once the adhesive 19 dries or is cured. Although this construction virtually guarantees permanent fixing of the yoke 10 on the CRT 12, the amount of adhesive 19 used makes this method somewhat messy and expensive.
It is therefore an object of the invention to construct a CRT/deflection yoke assembly that reliably holds the position of a deflection yoke on a CRT in a desired fixed position while minimizing the mess and cost associated with conventional adhesive-based assemblies.